1. Field of the Invention
The present invention relates generally to fibrous glass mats and more particularly to an improved fibrous glass mat especially suitable for use in roofing shingles and a method of making such a mat.
2. Description of the Prior Art
In the past, most asphalt roofing shingles were constructed of organic rag felt impregnated and coated with asphalt or other such bituminous substance, the rag felt, in most cases, being made on a cylinder paper machine. More recently, the demand for and production of this type of shingle has increased substantially. For example, in 1961, the industry produced and sold approximately 40 million squares of asphalt shingle for customer use. A square covers 100 square feet of roof area and, in 1961, cost the contractor approximately seven dollars. In 1971, approximately 57 million squares of asphalt shingles were produced and sold at a cost of about 9 dollars a square. The estimated industry production and sale of asphalt shingles in 1981 is approximately 74 million squares. It should be apparent from these figures that the asphalt roofing market is highly significant and growing at a rapid rate.
In responding to the aforestated increase in demand and production of asphalt roofing material, industry has found that the addition of new cylinder paper machines for producing rag felt is very expensive. Further, in depleting the supply of materials needed in making rag felt, the latter has itself become more expensive. For these reasons, industry has taken a look at other types of shingle mats and particularly mats made of fiber glass.
In developing a new type of glass mat especially suitable for roofing shingles, there are three basic objectives which should be achieved. Firstly, the glass mat should be inexpensive so that competitively priced shingles can be produced. Secondly, the glass mat should be uniform so as to avoid production discontinuity and waste which otherwise increases the manufacturing cost of the mat and therefore the shingle. Thirdly, the mat should display sufficient tearing resistance for maintaining integrity and resistance against blow-offs of the applied shingles under severe wind conditions.
Heretofore, the prior art has not satisfactorily met all three of the foregoing objectives. For example, one suggestion has been to provide a steam-blown glass fiber mat. While this type of mat is relatively inexpensive to manufacture, it has been found to display unsatisfactory tear resistance, thereby resulting in a shingle highly susceptible to blow-off. On the other hand, a dry forming process swirl reinforced mat utilizing a web of base fibers and swirled continuous glass filaments as reinforcement fibers has also been suggested by the prior art. While the latter type of mat has been found to display better tear resistance than the steam-blown mat, the dry process utilized in forming such a mat is expensive and slow. Due to relatively low production output and relatively high labor requirements utilized with this process, the ultimate product is relatively expensive. In addition, it has been found that this type of mat is not reliably uniform in production, resulting in production discontinuity and waste and therefore unnecessary cost and delay. For the most part, the prior art has been unable to produce such a mat other than by the dry process. This drastically limits the ability to adequately disperse the reinforcement fibers throughout the base fiber web, resulting in a limitation on the tear strength of the ultimately produced mat.
Even in view of the foregoing deficiencies, industry has continued to look towards glass mat for the production of asphalt shingles. For example, in 1961, the use of glass mat for this purpose was substantially non-existent. In 1971, approximately 250,000 squares of asphalt shingles with glass mat were produced and sold. The projection for 1981 is that approximately 11 million squares of asphalt shingle using glass mat will be produced and sold in that year. Because of this increased demand for roofing shingles and mat generally and glass mat in particular, competition in this field has become keener. In addition, the capability to produce a more economical and uniform mat with satisfactory tear resistance has become increasingly more important.
As will be seen hereinafter, the present invention has overcome many of the problems left unsolved in the prior art by providing a fibrous glass mat which is more economically and uniformly produced and which displays improved tear resistance. In this manner, a more economical and higher quality shingle can be produced.